No one wants to overeat. And certainly no one wants to overeat for years, become overweight, and end up with a high risk of diabetes or heart disease - yet two thirds of Americans do precisely that. Even though we know better, we often eat too much. Why does our behavior betray our own intentions to be lean and healthy? The problem, argues obesity and neuroscience researcher Stephan J. Guyenet, is not necessarily a lack of willpower or an incorrect understanding of what to eat. Rather, our appetites and food choices are led astray by ancient, instinctive brain circuits.